Wave transmission network



Dec. 8, 1942. A, LE ENT 2,304,545

WAVE TRANSMISSION NETWORK Filed Aug. 23; 1941 5 Sheets-Sheet 1 CL x4 31x4 RZR I R/ FIG. 7 ,4

INl ENTOR AW. CLEMENT ATTORNEY 1942- A. w. CLEMENT 2,304,545

WAVE TRANSMI S S ION NETWORK Filed Aug. 23, 1941 5 Sheets-Sheet 2 o- I Io A 2) F/G.8 5 w H619 ,4 TTOR/VEV 1366- v 1942- A. 'w. CLEMENT 2,304,545

' WAVE TRANSMISSION NETWORK Filed Aug. 25, 1941 3 Sheets-Sheet 5lNl/ENTOR By AW. CLEMENT A 7' TORNEV Patented Dec. 8, 1942 UNITEDSTATES' PATENT OFFICE 7 2,304,545 I WAVE TRANSMISSION I Andrew' W.Clement, Fortress Monroe, Va., assignor to Bell Telephone Laboratories,Incor- "porated, New York, N. Y., a corporation of New York ApplicationAugust 23, 1941, Serial No. 408,023 42 Claims. (Cl. 178-44) Thisinvention relates to Wave transmission networks and more particularly toa combined variable phase shifter and attenuator.

' An object of the invention is to combine the functions of a variablphase shifter and a variable attenuator in a single network.

' 7 Another object is to vary either the phase shift or the attenuationof a network without materially affecting the other characteristic.

, Another object is to vary either the phase shift or the attenuation ofa network without materially changing its image impedance.

A further object of the invention is to simplify the circuit of, andreduce the size and cost of,

' a .network in which both the phase shift and the attenuation may beindependently varied.

Heretofore, in wave transmission systems when it has been required tovary both the phase shift and the attenuation two independent networkshave been used. In accordance with the present invention there isprovided a single network in which both the phase shift and theattenuation may be varied, each substantially independently of theother, without materially afiecting the image impedance. The network isof the bridged-T type, comprising two equal reactive series impedancebranches, an interposed reactive shunt impedance branch and a reactivebridging impedance branch. A resistor is included in either the shuntbranch or the bridging branch, or preferably, each of these branches in-1 cludes a resistor. Each resistor may be connected either in series orin parallel with the impedance branch with which it is associated, orwith a portion thereof.

In order to vary the phase shift, means are provided for varying thereactances of two of the reactive impedance branches, either the twoseries branches or the shunt branch and the bridging branch, and thesemeans may be arranged for unitary control. In some cases it is necessaryto vary three reactances, for example the two series branches and thebridging branch. In order to vary the attenuation, the resistor orresistors ar made variable, and when two resistors are used, the meansemployed may also be under unitary control. An adjustment of the phaseshift through a considerable range will have but slight effect upon theattenuation and on the other hand, when two resistors are used,

an adjustment of the attenuation through a considerable range willchange the phase shift only slightly. Furthermore, the network may bedesigned to have an image impedance which is a constant, pure resistancover a wide frequency range and adjusting either the phase shift or theattenuation will not materially, change this impedance.

sistive load impedances.

The nature of the invention will be more fully understood from thefollowing detailed description and by reference to the accompanyingdrawings, in which like reference characters represent spective branchesand the series reactive impedance branches are made variable;

Fig. 2 shows another embodiment of the invention similar to Fig. 1except that the resistors are connected in series with their respectivebranches;

Fig. 3 is a circuit similar to that of Fig. 1 except that the reactancesof the bridging branch and the shunt branch instead ,of the seriesbranches, are made variable;

Fig. 4 shows a circuit similar to that of Fig. 3 except that theresistors are in series with their respective branches;

Fig. 5 is similar to Fig. 1 except that the resistor in the shunt branchis in series instead of in shunt therewith;

Fig. 6 is similar to Fig. 1 except that the resistor in the bridgingbranch is connected in series instead of in shunt;

Fig. 7 is similar to'Fig. 3 except that the resistor Fig. 11 issimilar-to Fig. 9 except the resistors are in series with theirassociated reactances;

Fig. 12 follows the circuit of Fig. 3, the series reactances beinginductors, the reactance in the bridging branch being a capacitor andthe reactance in the shunt branch being a second capacitor;

Fig. 13 is the same as Fig. 10 except the inductors are variable insteadof the capacitors;

Fig 14 is similar to Fig. 13 except that the A This. feature is ofimportance when the network i'sconnected between matching reoicapacitors has been replaced by its equivalent T;

Fig. is similar to the circuit of Fig. 12 except that an inductor hasbeen added in parallel with the bridging branch:

Fig. 16 is similar to Fig. 12 except the resistors are in series withtheir associated reactances instead of in parallel;

Fig. 17 is similar to Fig. 16 except an inductor has been added inseries with the shunt branch;

Fig. 18 is similar to Fig. 9 except the resistor and the inductor in theshunt branch are connected in series instead of in parallel;

Fig. 19 is similar to Fig. 9 except the resistor and the inductor in thebridging branch are in series instead of in parallel;

Fig. 26 is similar to Fig. 16 except the resistor and the capacitor inthe bridging branch are connected in parallel instead of in series; and

Fig. 21 is similar to Fig. 16 except the resistor and the capacitor inthe shunt branch are in parallel instead of in series.

Returning to Fig. 1, there is shown schematically a symmetricalbridged-T structure embodying the invention. The network has a pair ofinput terminals I, 2 and a pair of output terminals 3, 4 to whichterminal loads of suitable impedance may be connected. The T comprisestwo equal reactive impedance branches Xi and X2 connected in seriesbetween the input terminal I and the corresponding output terminal 3 andan interposed shunt impedance branch, consisting of a reactive impedanceX3 and a resistor RI in parallel, connected on one side to the commonterminal of the reactances XI, X2 and on the other side to the remaininginput terminal 2 and output terminal :l. The bridging branch, whichincludes a resistor R2 and a reactive impedance X4 in parallel, is alsoconnected between the terminals I and 3. The network is shown in itsunbalanced form, so that the path connecting terminals 2 and d may begrounded or otherwise fixed in potential, but it may, of course, bebuilt in the balanced form if desired.

The four reactive impedance branches XI, X2,

, X3 and X43 are designed as an all-pass bridged-T structure having animage impedance which is a constant, pure resistance at all frequenciesand the desired phase shift over the operating frequency band forcertain settings of the variable reactances XI and X2. The mid-frequencyof the operating range is usually placed at or near the point where thephase shift-frequency characteristic has the maximum slope. The phaseshift is varied by increasing or decreasing each of the reactances XIand X2 by the same amount. These reactances are made variable for thispurpose and they may be arranged for unitary control, as indicated.Varying the phase shift over a considerable range does not materiallyaffect the attenuation of the network and if this range is not great theimage impedance is not much infected.

The attenuation of the network is largely dependent upon the values ofthe resistors RI and R2 and these resistances are ordinarily largecompared to the image impedance. To increase the attenuation RI and R2are decreased by proportional amounts, and to decrease the attenuationthe resistances are increased by proportional amounts. In order toadjust the attenuation the resistors RI and R2 are made variable andthey may be arranged for unitary control as shown. Varying theattenuation over a considerable range does not materially affect eitherthe phase shift or the image impedance of the network. If largerdeviations in the image impedance are permissible either one of theresistors may be omitted in Fig. 1, or in any of the other figures.

The network of Fig. 2 is similar to the one shown in Fig. 1 except thatthe resistors RI and R2 are connected in series with their associatedreactive impedance branches instead of in parallel with them. In thiscase the resistors ordinarily have values which are small compared tothe image impedance and they areincreased by proportional amounts toincrease the attenuation and decreased by proportional amounts todecrease the attenuation.

The circuits shown in Figs. 3 and 4 are similar to those shown in Figs.1 and 2, respectively, except that the reactances X3 and X4 are variedinstead of XI and X2. In these networks the reactances are variedtogether in the same direction and by proportional amounts to adjust thephase shift.

The network of Fig. 5 is similar to the one of Fig. 1 except theresistor RI is connected in series with the reactance X3 instead of inparallel. To increase the attenuation RI is increased and R2 isdecreased but the product of RI and R2 is kept substantially constant.

The circuit shown in Fig. 6 is also similar to Fig. 1 but the resistorR2is in series with X4 instead of being in parallel. In this case RI isdecreased and R2 is increased to increase the attenuation.

The network of Fig. 7 is similar to the one shown in Fig. 3 except thatRI is in series with X3. To increase the attenuation RI is increased andR2 is decreased.

The circuit shown in Fig. 8 is'also similar to Fig. 3 except that R2 isconnected in series with X8. To increase the attenuation RI is decreasedand R2 is increased.

From the above, it is seen that the following general rules may bededuced as to the direction in which the resistors RI and R2 are to bevaried in order to vary the attenuation of the network:

1. If connected in series with its associated reactive lmpedance branchthe resistor is increased in value to increase the attenuation anddecreased in value to decrease the attenuation.

2. If connected in parallel with its associated reactive impedancebranch the resistor is decreased in value to increase the attenuationand increased in value to decrease the attenuation.

An advantage or the networks in which both of the resistors Bi and R2are connected in series with their associated reactances, or both areconnected in parallel therewith, is that both resistors are variedproportionally and in the same direction in making attenuationadjustments. In the other circuits, in which one resistor is in seriesand the other one is in parallel, the resistors must be variedoppositely and the product of the two resistances is kept substantiallyconstant for all settings. For the best image impedance this product iskept approximately equalto the square of the image impedance. Generally,it .is easier to design two variable resistors, with unitary control,which are to be varied in the same direction and proportionally thanresistors which are to be varied in opposite directions and inverselywith respect to a constant.

The remaining figures show, by way of example only, a number of specificembodiments of the invention, and these will now be described briefly, I

Fig. 9 is a combined variable phase shifter and attenuator following thegeneralized circuit shown in Fig. 1. The series reactances XI and K2 areconstituted, respectively, by the equal capacitors Cl and C2, the shuntreactance X3 is theinductor Li and the bridging reactance X4 is a secondinductor L2. The reactors just mentioned are formed into a phase shifterof the bridged-T type such as is shown, for example, in Fig. 13a ofUnited States Patent 1,735,052 to Nyquist, issued November 12, 1929, thedetailed design of which is given therein. The capacitors Cl and C2 aremade variable, under a unitary control, to provide an adjustment of thephase shift. The resistor Rl, connected in parallel with Ill, and theresistor R2, in parallel with L2, are made variable, under a unitarycontrol, to provide an adjustment of the attenuation.

The network shown in Fig. is the same as Fig. 9 except that aparallel-connected capacitor C3 has been added to the bridging branch.This type of phase shifter is shown, for example, in Fig. 130 of theabove-mentioned patent. In this case all three of the capacitors aremade variable under a unitary control.

The circuit of Fig, 11 is similar to Fig. 9 except work is permissiblefor a given variation of the attenuation, one of the resistors, eitherRI or R2,

may be omitted. If this is done, about twice the former variation in theresistance value of the remaining resistor is required, for a given Ichange in the attenuation. Furthermore, it only one variable resistor isused a somewhat larger change in the phase shift will occur for n agiven variation of the attenuation.

. What is claimed is:

l. A combined variable phase shifter and attenuator oi the bridged-Ttype comprising two reactive series impedance branches, an interposedreactive shunt impedance branch, a reactive bridging impedance branch, avariable resistor associated with one of the two last-mentioned branchesand means for varying the reactances of two of said branches.

2. A network in accordance with claim 1 in which said resistor isassociated with said shunt branch.

3. A network in accordance with claim 1 in which said resistor isassociated with said bridging branch,

4. A network in accordance with claim 1 in v which said resistor isconnected in series wit the resistors RI and R2 are connected in seriesFig. 13 except-that the A made up of the capacitors ,Cl, 02 and C3 hasbeen replaced by its equivalent T constituted by the capacitors C6, C1and C8. This circuit is shown, for example, in Fig. 13b of theabove-mentioned patent.

The circuit of Fig. 15 is similar to Fig. 12 ex-v cept that aparallel-connected inductor L5 has been added to the bridging branch, asshown for example, in Fig. 11 of the Nyquist patent.

The network of Fig. 16 is similar to the one shown in Fig. 12 exceptthat the resistors RE and R2 are connected in series, instead of inparallel, with their associated reactances.

The network shown in Fig. 17 is similar to Fig. 16 except that aninductor L6 has been added in-series With the shunt branch. This circuitis shown, for example, in Fig. 10 of the above-mentioned patent.

The circuit of Fig. 18 is similar to Fig. 9 except that the resistor R!and the inductor Ll in the shunt branch are connected in series insteadof in parallel.

The network shown in Fig. 19 is also similar to Fig. 9 except that theresistor R2 and the inductor L2 in the bridging branch are connected inseries instead of in parallel.

The circuit of Fig. 20 is similar to Fig. 16 except that the resistor R2and the capacitor C5 in the bridging branch are connected in parallelinstead of in series.

The network shown in Fig. 21 is also similar to the circuit of Fig. 16except that the resistor RI and the capacitor C4 in the shunt branch areconnected in parallel instead of in series.

As already mentioned, if a somewhat wider variation of the imageimpedance of the netits associated branch.

5. A network in accordance with claim 1 in which said resistor isconnected in parallel with its associated branch.

6. A network in accordance with claim 1 in which the reactances of saidseries branches are variable.

'7. A network in accordance with claim 1 in which the reactances of saidshunt branch and said bridging branch are variable.

8. A combined variable phase shifter and attenuator of the bridged-Ttype comprising two reactive series impedance branches, an interposedreactive sh'unt impedance branch, a reactive bridging impedance branch,two variable resistors included, respectively, in said shunt branch andin said bridging branch and means for varying the reactances of two ofsaid branches- 9. A network in accordance with claim 8 in which each ofsaid resistors is connected in series with its associated impedancebranch- 10. A network in accordance with claim 8 in which each of saidresistors is connected in parallel with its associated impedance branch.

11. A network in accordance with claim 8 in which one of said resistorsis connected in series with its associated impedance branch and theother of said resistors is connected in parallel with its associatedimpedance branch,

12. A network in accordance wtih claim 8 in which the reactances of saidseries branches are variable. r

13. A network in accordance with claim 8 in which the reactances li'fsaid shunt branch and said bridging branch are variable.

14. A network in accordance with claim 8 in which each of said seriesbranches includes a capacitor.

15. A network in accordance with claim 8 in which each of said seriesbranches includes a capacitor, said shunt branch include an inductor andsaid bridging branch includes a second inductor. I

16. A network in accordance with claim 8 in which each of said seriesbranches includes .a capacitor. said shunt branch includes an inductorand said bridging branch includes a second inductorand anothercapacitor.

17. A network in accordance with claim 8 in which each of said seriesbranches includes a capacitor, said shunt branch includes an inductor,said bridging branch includes a second inductor and one of saidresistors is connected in parallel with its associated impedance branch.

18. A network in accordance with claim 8 in which each of said seriesbranches includes a capacitor, said shunt branch includes an inductor,said bridging branch includes a second inductor and one said resistorsis connected in series with its associated impedance branch.

19. A network in accordance with claim 8 in which eachof said seriesbranches includes a variable capacitor.

20. A network in accordance with claim 8 in which each of said seriesbranches includes a variable capacitor and said capacitors are arrangedfor unitary control.

21. A network in accordance with claim 8 in which each of said seriesbranches includes an inductor.

22. A network in accordance with claim 8 in which each of said seriesbranches includes an inductor, said shunt branch includes a capacitorand said bridging branch includes a second capacitor.

23. A network in accordance with claim 8 in p which each of said seriesbranches includes an inductor, said shunt branch includes a capacitorand another inductor and said bridging branch includes a secondcapacitor.

24. A network in accordance with claim 8 in which each of said seriesbranches includes an inductor, said shunt branch includes a capacitor,said bridging branch includes a second capacitor and one of saidresistors is connected in series with its associated impedance branch.

25. A network in accordance with claim which said shunt branch includesa variable capacitor and said bridging branch includes a secand variablecapacitor.

26. A network in accordance with claim 8 in which said shunt branchincludes a variable capacitor, said bridging branch includes a secondvariable capacitor and said capacitors are arranged for unitary control.

2'7. A network in accordance with claim 8 in which said variableresistors are arranged for unitary control.

28. A network in accordance with claim 8 in which said means for varyingthe reactances are under unitary control.

29. A network in accordance with claim 8 in which said variableresistors are arranged for unitary control and said means for varyingthe reactances are under unitary control.

a in.

30. A combined variable phase shifter and at tenuator of the bridged-Ttype comprising two variable series capacitors, an interposed shuntimpedance branch including an inductor and a variable resistor and abridging impedance branch including a second inductor and a secondvariable resistor.

31. A network in accordance with claim 30 in which said bridging branchincludes a third capacitor.

32. A network in accordance with claim 30 in which said inductor andsaid resistor in said shunt branch are connected in parallel and saidsecond inductor and said second resistor in said bridging branch arealso connected in parallel.

33. A network in accordance with claim 30 in which said inductor andsaid resistor in said shunt branch are connected in series and saidsecond inductor and said second resistor in said bridging branch areconnected in parallel.

34. A network in accordance with claim 30 in which said variablecapacitors are arranged for unitary control.

35. A network in accordance with claim 30 in which said variableresistors are arranged for unitary control.

36. A network in accordance with claim 30 in which said variablecapacitors are arranged for unitary control and said variable resistorsare also arranged for unitary control.

3'7. A combined variable phase shifter and attenuator of the bridged-Ttype comprising two series inductors, an interposed shunt impedancebranch including a variable capacitor and a variable resistor and abridging impedance branch including a second variable capacitor and asecond variable resistor.

38. A network in accordance with claim 3''! in which said shunt branchincludes a third inductor.

39. A network in accordance with claim 37 in which said capacitor andsaid resistor in said shunt branch are connected in series and saidsecond capacitor and said second resistor in said bridging branch arealso connected in series.

40. A network in accordance with claim 37 in which said variablecapacitors are arranged for unitary control,

41. A network in accordance with claim 37 in which said variableresistors are arranged for unitary control.

42. A network in accordance with claim 37 in which said variablecapacitors are arranged for unitary control and said variable resistorsare also arranged for unitary control.

ANDREW 'w. CLEMENT.

